#include<stdio.h>
#include<math.h>
class Point
{
    public:
        Point(int xx, int yy){X = xx, Y = yy;}
        int GetX() const {return X;}
        int GetY() const {return Y;}
        friend float fDist(Point &a, Point &b);  //friend func
    private:
        int X, Y;
};
float fDist(Point &a, Point &b)
{
    float x = a.X - b.X;  //can use class private ptr.
    float y = a.Y - b.Y;
    float len = sqrt(x*x + y*y); 
    return len;
}
int main(int argc, char *argv[])
{
    Point a(1, 2), b(3, 4);
    printf("len is %f\n", fDist(a, b));
    return 0;
}
